UI reference

Lossy compression

Confirm a JPEG Baseline or lossy JPEG 2000 compression and set its quality.

Browser: available nowmacOS app: 1.4.0 or newer

This dialog opens when you run Compress series to JPEG Baseline (lossy)… or Compress series to JPEG 2000 (lossy)… from the command palette (⌘K / Ctrl+K). Lossy compression never runs without it.

Lossy compression changes pixel values for good. Do not use it where exact values matter, such as measurement, quantitative analysis or primary diagnosis. Use a lossless syntax for those.

JPEG quality (JPEG Baseline) runs from 50 to 100 and starts at 90. Higher values keep more detail and make larger files. JPEG Baseline holds 8-bit samples only, so 12-bit and 16-bit images are refused.
Target compression ratio (JPEG 2000) runs from 2:1 to 50:1 and starts at 10:1. The target is set against the stored bit depth, so the ratio written to the header, which is measured against the full sample size, can be higher.

Click Compress (lossy) to start, or Cancel to close the dialog without changing anything.

After encoding, every frame is decoded again and compared with the original stored values. If any frame’s peak signal-to-noise ratio (PSNR, peak at the full stored range) is below 30 dB, or the encoder fails, nothing is changed and a notice says why.

Each compressed instance gets:

Lossy Image Compression (0028,2110) set to 01.
The achieved ratio added to Lossy Image Compression Ratio (0028,2112), and ISO_10918_1 or ISO_15444_1 added to Lossy Image Compression Method (0028,2114). Values from earlier lossy steps are kept.
Image Type (0008,0008) changed from ORIGINAL to DERIVED.
A new SOP Instance UID. Study and Series Instance UIDs stay the same.

The audit log records the target, the quality setting, the achieved ratio and the lowest PSNR. Undo (⌘Z) restores the series.